Reactions with 5,6,7-Trihydro-5,7-diarylthiazolo [3,2-b] -s-triazin-3(2 H)-ones

Abstract

Condensation of thiourea with ammonium acetate or amine and aldehyde gives hexahydro-s-triazine-2-thiones 1-4 .4,6-Diarylhexahydro-s-triazine-2-thiones (1) which were prepared by AHMED and RAO 4 reacted with chloroacetic acid to give the corresponding 4,6-diaryl-2-carboxymethylthio-3,4,5,6-tetrahydro-s-triazines (2). Cyclisation of 2 by the action of acetic anhydride in acetic acid yields products which are formulated as 5,6,7-trihydro-5,7-diarylthiazolo[3,2-b]-s-triazin-3(2H)-ones (3). HN^^N rThe IR spectrum (KBr) of 3 a shows an intense CO band at 1770 cm -1 . This carbonyl frequency is rather high; however, it has been noted that a carbonyl group attached to a triazole and a triazine rings shows unusually high stretching frequency [5][6][7][8] . The NMR spectrum (DMSO-d6) of 3 a, shows a methylene group (s, 2H) at r 5.27 ppm. These facts indicate that the products 3 exist in the keto form, and not as the hydroxy form.The methylene group of compound 3 was found to condense with aromatic aldehydes to give 2-arylmethylene -5,6,7-trihydro -5,7-diary lthiazolo[3,2 -b] -s-triazin-3(2H)-ones (4). These arylmethylene derivatives were better prepared directly from the hexahydrotriazine-thiones by the action of chloroacetic acid, the aromatic aldehyde in the presence of acetic acid, acetic anhydride and sodium acetate. The carboxymethylthio-tetrahydrotriazines (2) also reacted with the remaining reagents to yield the arylmethylene derivatives (4).The IR spectrum of the arylmethylene derivative (4a) shows a carbonyl absorption at ca. 1730 cm -1 . This CO frequency has been shifted to a lower frequency compared with the CO frequency in 3, due to its conjugation with the exocyclic C=C double bond 9 .